1. Technical Field
This invention relates generally to photolithography and semiconductor formulation, and more specifically, to a non-polymeric, non-silicon containing molecular resist material and method of using the molecular resist for photolithographic imaging.
2. Background Art
Manufacturing of semiconductor devices is dependent upon the accurate replication of computer aided design (CAD) generated patterns onto the surface of a device substrate. The replication process is typically performed using lithographic processes followed by a variety of subtractive (etch) and additive (deposition) processes.
Photolithography, a type of lithographic process, is used in the manufacturing of semiconductor devices, integrated optics, and photomasks. The process basically comprises: applying a layer of a polymeric material containing a photoacid (PAG) that will react when exposed to light, known as a photoresist or, simply, a resist; selectively exposing portions of the resist to light or other ionizing radiation, i.e., ultraviolet, electron beams, extreme UV, X-rays, etc., thereby changing the solubility of portions of the material; and developing the resist by washing it with a developer solution, such as tetramethylammonium hydroxide (TMAH), thereby removing the non-irradiated (in a negative resist) or irradiated (in a positive resist) portions of the layer. A post-exposure bake may be employed to complete changing the solubility of portions of the material, before developing the exposed resist.
In a positive resist, the initially unexposed polymeric resist is insoluble in developer, while the exposed resist becomes more soluble as the exposure dose is increased above a threshold value. For a negative resist, similar behavior is observed, except that the initially unexposed polymeric resist is soluble in developer, and the exposed area is rendered insoluble. By means of this differential solubility between the exposed and unexposed resist areas, it is possible to form a pattern in the polymeric resist film. This pattern can be used to form integrated circuit devices, and is currently a critical component in their manufacture.
Despite the widespread use of polymeric resist materials, as the need for higher resolutions and minimum feature sizes increases, certain characteristics of polymeric resist materials may result in non-uniform pattern features. For example, the non-linear dissolution rates of some polymers, as well as the distribution of polymer chain lengths and chain entanglements, may lead to non-uniform feature dimensions and line edge roughness at very small feature sizes. In turn, such pattern variations may induce fluctuations in threshold voltages and line resistances, thereby degrading circuit performance.
Generally, high post-exposure bake temperatures (e.g., greater than 120° C.) are needed to change the solubility of portions of polymer containing resist material. As the need for higher and higher levels of integration has arisen in the industry, the need for higher resolution of the resist composition, i.e., a larger number of lines and spaces in a given area has increased dramatically. At high bake temperatures, acid-diffusion becomes pronounced which adversely affects the resolution of the images. Therefore, there is a need for a resist material, which when exposed undergoes a change in solubility at low post-exposure bake temperatures.